It is believed that technological barriers may exist for fabricating functional device structures with characteristic dimensions below 1 μm. These barriers may include problems in synthesizing the nano-sized structures in a sufficiently small dimension, in a specific pattern, or in a uniform size and spacing distribution. Furthermore, such nano-sized structures may require direct fabrication into microsystems to allow proper functioning. For example, a neural stimulatory microsystem may require fairly uniform nano-sized electrode arrays for use in focally stimulating neural tissue to treat blindness, as well as Parkinson disease, Huntington disease, and other neurological disorders. In one particular application, focal stimulation may require electrodes or groups of electrodes on the order of 100 nanometers or less, with spacing of no more that 5 microns to properly mimic the actions of rods and cones in the retina of the eye. Thus, overcoming the barriers to fabricating nano-sized structures may lead to developing a useful prosthesis device to restore lost vision associated with certain eye diseases, such as, for example, retinitis pigmentosa and perhaps macular degeneration.
Another difficulty in developing a controllable synthesis technology for making nano-sized structures may be attributed to the lack of systematic atomic level characterizations at various stages of the process. Detailed information regarding the geometric arrangement, lattice parameter, magnetic, electronic, and catalytic properties may be needed to understand the relationship between nanoscopic structures and their macroscopic properties. Additionally, the inability to obtain localized topographic, chemical, magnetic, and electronic information may further limit the realization of specific nanostructure characteristics.
It is believed that there have been efforts that have focused on single crystal surface studies to better understand the fundamental reaction mechanism, and to mimic the behavior of real catalysts. Such an approach is referred to in Oh, S. H., Fisher, G. B., Carpenter, J. E., and Goodman, S. W., “Comparative Kinetic Studies of Co—O2 and Co—NO Reactions over Single Crystal and Supported Rhodium Catalysts,” J. Catalysis, 100, 360, 1986 (“the Oh reference”) and Ng, K. Y. S., Belton, D. N., Schmieg, S. J., and Fisher, G. B., “NO—CO Activity and Selectivity over a Pt10Rh90(111) Alloy Catalyst in the 10-torr Pressure Range,” J. Catalysis, 146, 349, 1994 (“the Ng reference”). The Oh and Ng references indicate that the rate constants obtained from these single crystal surfaces may be used to model the reaction rates of high surface area catalysts. Such single crystal surface studies, however, merely represent the exposure of one crystal orientation, which foregoes potential opportunities offered by cluster-size effects.
It is believed that experiments have been performed to demonstrate the benefits of cluster-size effects. Such experiments may include the use of laser ablation and mass spectrometry to produce isolated clusters in a gas phase with a specific quantity of atoms, as referred to in Cox, D. M., Brickmnan, R., Creegan, K., and Kaldor, A., “Gold Clusters—Reactions and Deuterium Uptake,” Zeitschirift Fur Physik D-Atoms Molecules and Clusters, 19(1-4), 353, 1991 (“the Cox reference”) and Heiz U., Sherwood, R., Cox, D. M., Kaldor, A., and Yates, J. T., “CO Chemisorption on Monodispersed Platinum Clusters on SiO2 Detection of CO Chemisorption on Single Platinun Atoms,” Journal of Physical Chemistry, 99(21), 8730, 1995 (“the Heinz reference”). These references have indicated that for a certain unique number (N) of atoms in the cluster, the activity and/or selectivity may be orders of magnitude higher than clusters with a different number of atoms in the cluster. Gold nano-clusters, for example, with diameters less than 5 nanometers may have been developed by the Osaka National Research Institute. As referred to in Haruta, M., “Size- and Support-dependency in the Catalysis of Gold,” Catalysis Today, 36(1), 153, 1997 (“the Haruta reference”), such gold nano-structures may exhibit extraordinarily high activity and/or selectivities in a variety of reactions, including the reactions of CO and hydrogen oxidation, decomposition of amines and organic halogenated compounds, and reduction of nitrogen oxides, among others.
Two dimensional macromolecular structures of MoS2 and WS2 in the form of nanotubes and cylinders are referred to in Chianelli, R. R., Berhault, G., Santiage, P., Mendoza, D., Espinosa, A., Ascencio, J. A., Yacaman, M. J., “Synthesis, Fundamental Properties and Applications of Nanocrystals, Sheets, Nanotubes, and Cylinders based on Layered Transition Metal Chalcogenides,” Materials Technology, 15(1), 54, 2000 (“the Chianelli reference”). The edge sites and basal plane sites of theses structures may have distinctive catalytic behavior including special activities and/or selectivities, as referred to in Chianelli, R. R., Daage, M., and Ledoux, M. J., “Fundamental Studies of Transition-metal Sulfide Catalytic Materials,” Advances in Catalysis, 40, 177, 1994 (“the Daage reference”).
Furthermore, efforts to use various chemical synthetic approaches to produce uniform nano-crystallites may involve the use of sol-gel processing, controlled reduction in micro-emulsions, and electrochemical reduction, as referred to in Reetz, M. T. Heilbig, W., Quaiser, S. A., Stimming, U., Breuer, N., and Vogel, R., “Visualization of Surfactants on Nanostructured Palladium Clusters by a Combination of STM and High-resolution TEM,” Science, 267, 367, 1995 (“the Reetz reference”). Such efforts may, however, result in a distribution of particle size that may preclude a well-defined surface for activity-selectivity studies. Without a uniform surface, the nature of active sites may not be fully elucidated because the true catalytic active sites may constitute a very minute portion of the surface.
It is therefore believed that these studies demonstrate a need for improved methods for fabricating nano-scale catalytic devices. The challenges to fabricate such nano-sized catalysts may, however, include the ability to produce sufficiently stable structures and/or control their synthesis when using the above cited approaches. Although there may have been some ability to produce monodispersing nano-particles in solution, it is believed that dispersing these particles on a support surface in a uniform manner is problematic and therefore a challenge. Accordingly, it is believed that a need may exist for uniform and stable nano-sized catalyst device structures and a method to fabricate them.
It is also believed that the trend toward miniaturizing magnetic recording media may pose further challenges, as well as opportunities, for applications involving nano-sized structures. As referred to in Kryder, M. H., “Ultra High Density Recording Technologies”, MRS Bull. Vol. 21, (9), 17(1996) (“the Kryder reference”), it has been predicted that the density of magnetic recording may reach 10 to 100 Gbits/inch during the years between 2001 and 2005. The magnetic particles in the next generation magnetic recording materials may therefore need to be ever smaller, which may be on the order of approximately 10 nanometers in size, while also remaining magnetically “hard” and moderately isolated.
With the miniaturization of magnetic technologies, the need to understand magnetization on this small scale may become increasingly important as referred to in Chou, S. Y., Kraus, P. R., and Kong, L., “Nanolithographically defined magnetic structures and quantum magnetic disk”, J. Appl. Phys. 79, 6101 (1996) (“the Chou reference”) and Leslie-Pelecky, D. L., Rieke, R. D., “Magnetic Properties of Nanostructured Materials”, Chem. Mater. 1996, 8, 1770-1783 (“the Leslie-Pelecky reference”). The Leslie-Pelecky reference may suggest that the need to study the static and dynamic magnetic properties of nano-sized structures may be critical to their realization, particularly in the context of regular dot arrays. Major impediments to understanding the cooperative effects on the nanometer scale may include, for example, the ability to fabricate well-controlled magnetic nano-sized structures. Also, recent advances in characterizing and controlling grain size and intergranular distance of the magnetic materials may generate interest in exploring new synthesizing techniques, in which the orientation and crystalline structure of magnetic nano-sized crystals may be precisely influenced. In particular, it is believed that a fabrication technique to control these structural parameters, orientation and crystalline structure of magnetic nano-sized crystals may be especially desirable.
During the “Eye and the Chip” Symposium on Artificial Vision (Jun. 16 & 17, 2000), Dr Gregory W. Auner gave a conference in which he displayed a picture of a nanostructure formation, and indicated that work was progressing in this area towards achieving a suitable construction for retinal implantation.